Technical Field
The present invention relates generally to PEGylated aspartyl-tRNA synthetase (DRS) polypeptides, compositions comprising the same, and methods of using such polypeptides and compositions for treating or diagnosing a variety of conditions.
Description of the Related Art
Aspartyl-tRNA synthetases (DRS), and fragments and variants thereof, (collectively DRS polypeptides) have recently been shown to possess a variety of non-canonical activities of therapeutic and diagnostic relevance. In particular it has been established that certain aspartyl-tRNA synthetase fragments are highly potent, endogenously produced, Toll-like receptor modulators. Without being bound to any one specific theory of operation, it is believed that such DRS polypeptides are released from macrophage cells upon proteolytic cleavage, or through alternative splicing of the full length AspRS tRNA synthetase and are capable of binding to and modulating the activity of immunomodulatory, and other cell types. Such DRS polypeptides when administered, provide for a novel mechanism of selectively modulating inflammatory responses, without the side effect profiles typically associated with traditional anti-inflammatory agents such as steroids
Toll-like receptors (TLRs) are a family of pattern recognition receptors that play a key role in initiating the rapid innate immune response in an organism. TLRs recognize certain pathogen or host derived cellular components which can be generally characterized as being either pathogen associated molecular patterns, (PAMPs), or damage-associated molecular pattern molecules, (DAMPS) respectively. PAMPS are typically unique to a given class of pathogen, and include for example bacterial components such as the lipopolysaccharide of Gram negative bacteria, and viral specific nucleic acid motifs or viral specific modifications of RNA or DNA. By contrast DAMPS are typically endogenous molecules released from dying host cells upon cellular stress or tissue damage.
TLRs are implicated in several chronic inflammatory and immune mediated disorders by various potential mechanisms, including those in which infectious agents have been proposed to initiate disease progression. For example in scenarios in which endogenous damage signals or self-antigens cause chronic inflammation in a TLR dependent manner, or where TLRs may be involved in the breakdown of immune tolerance. TLRs have been implicated in the pathogenesis of chronic inflammatory diseases such as inflammatory bowel disease, rheumatoid arthritis, psoriasis, and multiple sclerosis.
It is now increasingly recognized that the successful treatment of some autoimmune and inflammatory conditions of tissues requires effective control of the inflammatory reaction in order to preserve tissue integrity and function, without immune-compromising the patient. Recent experimental evidence has shown that specific modulation of TLR pathways induces an improvement in several inflammatory conditions, without comprising tissue function, or enhancing bacterial or viral infections, suggesting the potential for new therapeutic anti-inflammatory strategies with significantly improved side effect profiles. Moreover TLR agonists have already proved useful in clinical trials in allergic, infectious and autoimmune diseases and are under development for a broad range of other diseases including cancer, arthritis, multiple sclerosis, inflammatory bowel disease, see generally Zhu and Mohan (2010) Mediators of Inflammation doi:10.1155/2010/781235; Hennessy et al., Nat. Rev. 9:293-307, 2010). Therefore TLRs are becoming increasingly recognized as novel potential therapeutic targets for the modulation of a broad variety of diseases and disorders.
To best exploit these and other activities in therapeutic or diagnostic settings, there is a need in the art for DRS polypeptides having improved pharmacokinetic properties. The present invention is focused on the development of DRS polypeptides that have been modified through the addition of water soluble polymers, which retain the biological activity of the native DRS polypeptides and exhibit superior pharmacokinetic and other properties.
Although many suitable water soluble polymers exist, polyethylene glycol (PEG) is typically preferred as a water soluble polymer for attachment because it has good solubility in both water and in many organic solvents, lacks of toxicity, and immunogenicity, and is also clear, colorless, odorless, and chemically stable.
The term “PEGylation” refers to the modification of biological molecules by covalent conjugation with polyethylene glycol (PEG). PEGylation can change the physical and chemical properties of a biological molecule, such as its conformation, electrostatic binding, hydrophobicity, and pharmacokinetic profile. In general, PEGylation improves drug solubility and decreases immunogenicity. PEGylation also increases drug stability and the retention time of the conjugates in blood, and reduces proteolysis and renal excretion, thereby allowing a reduced dosing frequency. In order to benefit from these favorable pharmacokinetic consequences, a variety of therapeutic proteins, peptides, and antibody fragments, as well as small molecule drugs, have been PEGylated.
These improved therapeutic forms of the DRS polypeptides enable the development of more effective therapeutic regimens for the treatment of various diseases and disorders, and require significantly less frequent administration than the unmodified proteins.